Subsea Power Research Articles

In-situ tensile and fatigue behavior of electrical grade Cu alloy for subsea cables

Distribution of electrical energy through subsea power cables has an increasingly important role in the renewable power generation. The majority of the subsea cables uses copper (Cu) as a conductor material. Cables suspended from sea level to sea floor are subjected to both static and cyclic loads that can introduce microstructural damage due to fatigue, creep and their interaction. In addition, since the manufacturing process of the stranded conductor results in Cu-materials with superficial irregularities and metallurgical anisotropy, the material performances need to be carefully addressed in order to reliably assess the wires life. In order to provide a deeper insight into the occurring damage mechanisms, monotonic and cyclic tests of micro-sized Cu tensile specimens were carried out using in-situ micromechanical testing, inside a scanning electron microscopy (SEM) equipped with an electron backscatter diffraction. Tensile and cyclic loading behavior are discussed in correlation with the damage mechanisms observed directly and post-mortem. The twin boundary fraction in the microstructure is found to be linked to the deformation status, and thus can potentially be used as an indicator for predicting the remaining life of the material under service conditions.

Ferroresonance and Self-excitation Phenomena in Subsea Power Systems Considering Voltage Control Dynamics and Cable Constructive Parameters

Ferroresonance and Self-excitation Phenomena in Subsea Power Systems Considering Voltage Control Dynamics and Cable Constructive Parameters

E&P Notes (January 2022)

E&P Notes (January 2022)

Simulation of peak tension loads in Subsea power cables during installation

At present, most of the insurance claims in the offshore wind industry are due to cable failures where a large percentage occurs during the installation of the array and export cables. As the reliability of the cables depends on the location and installation method, it is important to map the risks involved, which can compromise the cable’s integrity in individual projects. This paper presents sensitivity analyses conducted on crucial parameters in the cable laying process, with an objective of successful installation of subsea power cables without any damages to the cable. The analyses focus on the peak tension loads with reference to key parameters as cable self-weight and laying geometry, as well as the cable deployment position on the installation vessel. Finite element analyses were conducted with both static forces and dynamic forces for irregular vessel motions, by the aid of the well-tested software OrcaFlex.

Effect of geometrical irregularities on fatigue of lead sheathing for submarine high voltage power cable applications

High voltage subsea power cables are typically composed of several layers, including: a conductive core, a dielectric layer, a ductile metallic watertight barrier and a series of radial and axial armours and polymer layers. The watertight barrier serves the purpose of preventing water permeating to the dielectric due to the outer layers' polymer hygroscopicity. Water impregnation may cause dielectric breakdown, with fatal consequences on the integrity of the power cable. The watertight barrier is made of extruded lead alloy and is subjected, during the installation and operational life of the component, to axial and radial displacement-controlled fatigue which might lead to cracking, thus to a loss of its isolating properties. Lead, due to the low melting temperature, is characterized by creep deformation and damage even at room temperature. A steel tape is winded around the polyethylene sheathing surrounding the lead barrier, which is deformed, and a helical ridge is generated. This irregularity causes a local concentration of strain which might potentially lead to early failure of the lead sheathing. In this work the results of displacement-controlled fatigue testing at different strain rates of sheathing material including the irregularity is presented and compared to the results in equivalent conditions, but in the absence of the irregularity. The strain concentration caused by the defect is analysed with the implementation of a creep material model calibrated on the cyclic properties of the alloy and the notch sensitivity of the material for the class of defects, temperature and frequency in exam is obtained. The results are applied to the modelling of the stress-strain field in the component with and without irregularity and conclusions are drawn on the danger that such irregularities pose on the structural integrity on the power cable.

A modelling evaluation of electromagnetic fields emitted by buried subsea power cables and encountered by marine animals: Considerations for marine renewable energy development

The expanding marine renewable energy industry will increase the prevalence of electromagnetic fields (EMFs) from power cables in coastal waters. Assessments of environmental impacts are required within licensing/permitting processes and increased prevalence of cables will increase questions concerning EMF emissions and potential cumulative impacts. It is presumed that protecting a cable by burial, may also mitigate EMF emissions and potential impacts on species. Focussing on a bundled high voltage direct current (HVDC) transmission cable, we use computational and interpretive models to explore the influence of cable properties and burial depth on the DC magnetic field (DC-MF) potentially encountered by receptive species. Greater cable pair separation increased the deviations from the geomagnetic field and while deeper burial reduced the deviations, the DC-MF was present at intensities perceivable by receptive species. An animal moving along a cable route may be exposed to variable EMFs due to varied burial depth and that combined with an animal's position in the water column determines the distance from source and EMF exposure. Modelling contextually realistic scenarios would improve assessments of potential effects. We suggest developers and cable industries make cable properties and energy transmission data available, enabling realistic modelling and environmental assessment supporting future developments.

Analysis of Subsea Energy Supply Systems for Improved Maintenance Using ANFIS and TOPSIS

The maintenance plan for the subsea energy supply system during the operation was optimized by firstly training the Adaptive Neuro-Fuzzy Inference System (ANFIS) model with historical data of process variables of the system such as voltage, current, power, and pressure in MATLAB software and then predicting the optimum output of the process using the trained model, which showed a good prediction of operational data after two cycles of computational analysis. The outputs from the trained model, coupled with expert opinions on historical data, were used to develop a Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) multi-criteria algorithm to select the best maintenance strategy. The reliability-centred maintenance, with a performance score of 0.811, ranked best amongst the maintenance strategies under the studied scenario. The result shows that the procedure could be applied in condition monitoring of operational subsea energy supply systems to predict impending faults through deviation error and prevent failure by the application of an appropriate maintenance strategy. Keywords: ANFIS, TOPSIS, Maintenance plan, Fault prediction and Subsea power supply systems DOI: 10.7176/ISDE/12-2-02 Publication date: April 30 th 2021

Characteristics study of post weld heat treatment in SA 387 grade 22 steel by cladding using gas tungsten arc welding process

SA387 Grade 22 steel material is designed for high mechanical strength and high pressure applications. Residual stress is the unwanted phenomenon in cladded SA387 Grade 22 steel in power plant and gas refineries applications. This residual stress can be reduced by the post weld heat treatment process. Similarly corrosion is another problem because of the reaction with the elements in the environment. These problems may be solved by imparting with a layer of corrosion resistant material deposition by means of cladding. Cladding is an economic solution to those problems. But the lifetime of SA387 Grade 22 steel has been reduced due to poor corrosion resistance against subsea water and residual stress. So the essential thickness of the SA387 Grade 22 steel is reduced due to corrosion and it may cause failure of the product used for high pressure applications. In this experiment, the reduced thickness of SA387 Grade 22 steel specimen is compensated by ER80S-B2 electrode material using gas tungsten arc welding (GTAW) process. ER80S-B2 electrode material provides resistance to reabsorption of moisture and in addition to this a high corrosion resistance ERNiCrMo2 material has been deposited over ER80S-B2 welded material by gas tungsten arc welding (GTAW). After deposition on the remanufactured material, the specimen is tested for its effectiveness in resisting corrosion to withstand subsea power plant and gas refineries applications.

Tape winding angle influence on subsea cable sheathing fatigue performance

A fundamental component of subsea power cables is the thin galvanized steel tape winded around the dielectric and sheathing layer in order to prevent permanent thermal cycling induced deformation. The pressure state induced by the resistance offered by such tapes against radial reformation reduces the triaxiality ratio of the stress state of the lead sheathing layer. It is known that a reduced triaxiality has a beneficial effect on ductility and fatigue life of metals. In the present work a series of finite element simulations are performed in presence of galvanized steel tapes at three different winding angles and without such reinforcement at all, obtaining a qualitative indication of its effect on the stress state induced in the sheathing layer. Loading conditions as internal pressure related to thermal dielectric expansion and cable bending are modelled. The numerical qualitative results are discussed in connection to a series of full-scale fatigue tests performed on subsea power cables with and without the support of steel tapes.

A 10‐kV SiC‐MOSFET (Gen‐3) Half‐Bridge Module‐Based Isolated Bidirectional DC–DC Converter Block for Medium‐Voltage High‐Power Applications

The packaging technology for the medium‐voltage silicon carbide (SiC)‐metal oxide semiconductor field‐effect transistor (MOSFETs) has come a long way since its inception. Now, it is feasible to design half‐bridge power modules based on 10‐kV SiC‐MOSFETs for higher current applications. This paves the way for many application areas for these devices, particularly for medium‐voltage and high‐power applications. This paper presents a design of a modular medium‐voltage, high‐power isolated DC–DC converter enabled by these 10‐kV SiC‐MOSFETs‐based power modules. The design objectives are targeted at increasing the efficiency, power density, and interoperability. The proposed DC–DC converter is aimed for applications like DC distribution for the data centers, subsea power transmission, offshore wind farms, and photovoltaic energy transmission–distribution–coordination; electric ship DC power transmission; solid‐state distribution transformer, etc. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Reliability test for subsea power semiconductors

Following the demand from a new domain of application, a test setup was developed to evaluate the performance of high-power semiconductor device when exposed to a dielectric liquid and high pressure. The specific test conditions were established to emulate the conditions inside a tank place in a deep-sea environment. Those conditions can be characterized by two key parameters: the pressure and the chosen dielectric/thermal liquid. The power semiconductor device is to be tested at high and low temperature to simulate operation under maximum load as well as when turned off, respectively. The reliability tests outlined here serve to support the development and the validation of Subsea technology for semiconductors power modules.

Environmental Permitting and Compliance Cost Reduction Strategies for the MHK Industry: Lessons Learned from Other Industries

The marine and hydrokinetic (MHK) industry plays a vital role in the U.S. clean energy strategy by providing a renewable, domestic energy source that may offset the need for traditional energy sources. The first MHK deployments in the U.S. have incurred very high permitting costs and long timelines for deploying projects, which increases project risk and discourages investment. A key challenge to advancing an economically competitive U.S. MHK industry is reducing the time and cost required for environmental permitting and compliance with government regulations. Other industries such as offshore oil and gas, offshore wind energy, subsea power and data cables, onshore wind energy, and solar energy facilities have all developed more robust permitting and compliance pathways that provide lessons for the MHK industry in the U.S. and may help inform the global consenting process. Based on in-depth review and research into each of the other industries, we describe the environmental permitting pathways, the main environmental concerns and types of monitoring typically associated with them, and factors that appear to have eased environmental permitting and compliance issues.

Fault detection method in subsea power distribution systems using statistical optimisation

Developing automation solutions that enable remote communications, monitoring and control for subsea applications are key steps in designing subsea power distribution systems. These systems require fast local control to protect the multiple electrical loads and the capability of transferring prompt real-time trip signals. This study introduces a data-driven distributed fault detection and identification algorithm to monitor multiple subsea loads. The proposed scheme is divided into three steps. First, a stochastic hidden-Markov model (HMM) is developed to model the dynamic evolution of different potential conditions of multiple subsea loads. Simultaneously, the second step computes a model of the transition probability between the current operating condition and the potential response of an individual load. In the third step, using real-time measurements, the HMM is updated to predict an unobserved degradation of the load's current condition. This is achieved through an integrated perturbation analysis and sequential quadratic programming method. An assessment of case studies on subsea AC power system is presented, which includes different subsea motor loads for compressors and pumps. Results show robustness against uncertainty in measurement noise and changes in equipment mean time between failures, providing enhanced reliability.

The challenge of data in analysis for infrastructure projects

Computational mechanics is both an area of active research and a powerful tool for practitioners. Most analysis in infrastructure is for projects where the resources available for the analysis are limited. The analysts must overcome challenges to complete projects on time and on budget. One of the greatest sources of challenges for analysts is the data used in projects but this source is not often discussed explicitly. There are three key challenges relevant to the data: incompleteness, uncertainty and appropriateness. A case study of a subsea power cable for an offshore wind farm demonstrates how these challenges arise in practice. A look to the future shows that there is much to do, but also much to expect.

Investigation of Power Supply to Subsea Loads from High Voltage Electric Source Using Modular Direct Current Scheme

Subsea power converters have been identified in recent researches as a potential means of supplying power to subsea loads and this technology has been seen as a means to reduce the reliance on offshore platforms. This study analyses all electric subsea high power system for power generation and transmission in the offshore oil and gas industry for sustainable subsea development. In order to accomplish the analysis of power generation and transmission to subsea loads, the MAT lab SIMULINK software was employed to ascertain losses arising from the transmission of power to subsea systems. Data from Agbara and Akpo fields, all located in Nigeria, were analysed using the MSDC model as an alternative power source for power generation and transmission to all subsea loads. When the voltage loss between a step out distance at 30 km and 200 km was compared for the Akpo oil field, the plots indicate a significant loss in voltage. The RMS value of voltage loss increased from 0.8874 at a step out distance 30 km to 0.9449 for 200 km.

Subsea power cable sheathing: an investigation of lead fatigue performance

The protection of subsea power cables against electrical failure is achieved by the use of a watertight layer. Due to its properties of chemical stability and ductility, lead has been the material of choice for this purpose for several decades. Due to the low melting temperatures of lead alloys, their behaviour is strongly influenced by time-dependent phenomena, such as creep and recrystallization, which become more prominent for lower strain rate deformations. In order to understand the performance of the alloys of interest under cyclic loading experienced during and after installation in combination with the different variables influencing its behaviour, extensive testing is necessary. This manuscript presents the results of fatigue tests at two different strain rates for an alloy of industrial interest. The tests are monitored with the aid of digital image correlation, which greatly reduces the uncertainty on the quantification of the real strain field. The post-mortem fracture surfaces are investigated through scanning electron microscopy and metallurgical characterization to help understanding the differences in the failure modes active in the different stress/strain regimes.

Tensile and fatigue behavior of a Pb-Sn-Sb alloy investigated via small-scale in-situ mechanical testing in SEM

Pb-Sn-Sb alloys (E-alloy) are commonly used in subsea power cable sheathing. Due to the relatively low melting temperature, i.e. around 600 K, this type of alloy is prone to experience microstructural time-dependent evolution such as recovery, relaxation, recrystallization and creep deformation even at room temperature, in contrast to other conventional materials for which involve these mechanisms are activated only at high temperatures. To better understand the deformation mechanisms of Pb-Sn-Sb alloys, small-scale in-situ mechanical testing inside a scanning electron microscope (SEM) has been conducted under both monotonic loading and cyclic loading conditions. Thanks to the in-situ imaging technique, the deformation behavior as well as the damage mechanisms were revealed with high resolution. The possible deformation mechanisms, including the creep behavior, has been discussed and the results can provide necessary input to damage calculations and modelling work of the studied alloy system used for cable sheathing.

JIP Prepares for Final Shallow-Water Test of Subsea Power System

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper OTC 29550, “ABB Subsea Power JIP—Going the Distance,” by Stian Ingebrigtsen, Svein Vatland, John Pretlove, and Henning Nesheim, ABB, prepared for the 2019 Offshore Technology Conference, Houston, 6–9 May. The paper has not been peer reviewed. Copyright 2019 Offshore Technology Conference. Reproduced by permission. A joint industry project (JIP) comprising ABB, Equinor, Total, and Chevron, is developing technologies for subsea power transmission, distribution, and conversion. The output will form a critical part of future advanced subsea-field developments. Begun in 2013, the project reached a major milestone in late 2017 when the first full-scale prototype of the variable-speed drive (VSD) passed a shallow-water test (Fig.•1). Final preparations are now underway for a 3,000-hour test of the complete subsea power system with two VSDs in a parallel configuration combined with subsea switchgears and controls.•The complete paper highlights elements of the technical development and an overview of the primary building blocks of the system, and presents in detail some of the challenges in developing, designing, and testing the•control system. Introduction A subsea power transmission and distribution system will enable an entire oil or gas production system to be placed directly on the seabed, allowing expansion of development to deeper and more-remote locations while yielding cost and safety benefits from reducing significantly, or even eliminating, the need for topside installation. The JIP is developing three products for the system: Subsea VSD Subsea medium-voltage (MV) switchgear Subsea control and low-voltage (LV) distribution Providing a technical solution that is realistic, possible to engineer, tolerant of extreme environments, and reliable in its performance presents a significant challenge. The equipment—the MV switch-gear, control and LV distribution, and the VSDs—must be able to run without intervention for many years. The equipment is qualified for water depths to 3000 m and will have capacity of up to 100•MW with a transmission distance of up to 600 km. The primary focus thus far has been to qualify the basic building blocks to serve the typical voltage and power ratings for subsea processing. All project-qualification activities follow the recommendations and technology readiness level (TRL) stages defined in DNV Recommended Practice (RP)-A203, applicable for components, equipment, and assemblies in hydrocarbon exploration and exploitation offshore. This RP provides a systematic approach to ensure that the technology will function reliably within specified limits, and it provides a common understanding and terminology of technology status and risk management. Other important aspects of the RP include the ability to identify required design changes at an early stage and to improve confidence in the new technology by close interactions and traceable•documentation. To ensure compact and reliable solutions, oil-filled pressure-compensated tanks are used for enclosure of the VSD and switchgear. All components are tested extensively under the full pressure they will experience at the target water depth. A high-level objective of the project is to design the equipment to minimize production downtime and the number of retrievals.

Range extension for electromagnetic detection of subsea power and telecommunication cables

ABSTRACT Subsea cables protection afforded by burying a cable [beneath the sea bed] also means that the available methods for their survey are drastically reduced. From the existing methods only electromagnetics (EM) detection can penetrate the sea bed and provide an effective means for cable localisation. However, EM waves attenuate faster in conductive media such as sea water. EM localisation is considered a short range detection mechanism requiring the use of autonomous or remotely operated underwater platforms. In this paper, the authors investigate the range of EM detection and test detection distances exceeding one hundred metres. The EM signal was detected at distances around 140 m in sea water during the trials conducted in a ‘real’ environment at Hooe Lake in Plymouth.

ABB and Siemens test subsea power grids: Putting a power-distribution station on the ocean floor could allow more raw materials to be processed down there - [News

ABB and Siemens test subsea power grids: Putting a power-distribution station on the ocean floor could allow more raw materials to be processed down there - [News